While 20–25 grams seems like a reasonable number based on the available data, this number does not account for muscle mass. It would make sense that people with greater lean body mass might have an increased capacity for amino acid uptake, which may in turn increase the amount of amino acids required after exercise for maximal MPS stimulation. In a recent study, researchers tested the idea that lean body mass may influence protein requirements for a maximal MPS response after exercise.

Previous studies have shown that 20–25g protein is enough to stimulate maximal increases in protein synthesis (MPS) after weight training. The present study challenged this conclusion, testing the idea that those with greater lean mass require more protein to stimulate maximal MPS after training.

Who and what was studied?

Researchers recruited 30 healthy males undergoing concurrent resistance training programs (two or more sessions per week for the previous six months). Participants were grouped according to their lean body mass. Those that had a lean body mass (LBM) less than or equal to 65 kilograms (143.3 pounds) were categorized as the low LBM group and those with a LBM of 70 kilograms or more (154.3 pounds) were categorized as the high LBM group. LBM was measured by dual-energy x-ray absorptiometry (DEXA).

The study had a randomized, double-blind crossover design, with the general setup laid out in Figure 1. Each participant took part in two trials designed to measure MPS after whole-body resistance exercise and whey protein ingestion. In two separate trials separated by two weeks, participants ingested 20 grams or 40 grams of whey protein isolate dissolved in water immediately after exercise. To control for diet and physical activity, all participants completed a three-day weighed food diary that was analyzed with nutritional analysis software. Control diets were then designed that were tailored to the individual’s food preferences while matching the energy intake and macronutrient composition of their habitual diet. Participants also completed a seven-day activity diary and were required to keep their activity consistent during the study period.

To measure MPS, participants were infused with an isotope-labeled amino acid tracer ( L-ring-13C6 phenylalanine) that was later detected in protein obtained from muscle biopsies. By measuring the incorporation of the labeled tracer after training, the researchers were able to quantify MPS. One hour after starting the tracer infusion, participants performed a whole-body resistance training routine consisting of three sets of 10 reps with a fourth set to failure. Exercises included chest press, lat pull-down, leg curl, leg press, and leg extension. Training loads were 75% of a participant’s one-rep maximum with one-second concentric and two-second eccentric contractions.

Immediately after exercise, skeletal muscle biopsies were obtained from the vastus lateralis (quadriceps) muscle. Participants then consumed the protein drink enriched with the isotope-labeled tracer. Subsequent biopsies were taken from the same leg 180 and 300 minutes after exercise. Arterial blood was also sampled for analysis 60 minutes prior to exercise, immediately before exercise, and several times 30 to 300 minutes after exercise. Plasma samples were analyzed for blood amino acid levels. To measure the activation of protein synthesis signaling, p70 ribosomal S6 kinase 1 (p70S6K1) activity levels were assessed from muscle biopsy samples.

Resistance-trained male subjects were divided into two groups of higher or lower lean body mass. In two separate trials, MPS was measured after ingesting 20 or 40 grams of whey protein following exercise, to test the idea that those with greater lean body mass require more protein for maximal post-exercise MPS.

What were the findings?

Contrary to the hypothesis that lean body mass affects the amount of protein required for maximal MPS, there was no significant interaction between protein dose and lean body mass group. In other words, MPS changes were similar between both groups at the two different dosages. On the other hand, when all participants were combined (as shown in Figure 2), a statistically significant change was observed. MPS was 20% higher with 40 grams of whey protein compared to 20 grams of whey protein after whole-body weight training, when not accounting for differences in lean body mass.

Moreover, MPS was greater with 40 grams of protein at both the 180 and 300 minute time-points, irrespective of lean body mass, as shown in Table 1.

Muscle leucine concentrations were greater with 40 grams compared to 20 grams of whey protein at 180 and 300 minutes. This makes sense, since leucine is a potent activator of cell signaling pathways that control protein synthesis. Interestingly, intracellular leucine levels were higher in low LBM than high LBM groups with both doses combined. As shown in Figure 3, there was no difference in p70S6K1 activity with the different protein doses. However, the low LBM group did show greater p70S6K1 activation at the 180 minute time-point, which may be attributed to greater concentrations of intracellular leucine.

LBM did not factor into the protein requirement for maximal MPS. This study showed that 40 grams of protein induced greater MPS than 20 grams in both high and low LBM groups, contradicting previous studies suggesting that MPS after exercise is maximized after ingesting 20–25 grams of high-quality protein.

What does this study really tell us?

Overall, a 40-gram dose of whey protein isolate taken immediately after training stimulated MPS to a greater extent than a 20-gram dose.

Contrary to the authors’ hypothesis, lean body mass did not influence the amount of protein required for maximal MPS activation. This contrasts with previous work suggesting that only 20–25 grams of whey protein is required for maximal MPS. Although more research is needed to determine the exact reason(s) for the lack of agreement here, differences in study design may be a key factor. Two of the studies that came to the consensus that 20–25 grams of protein stimulates maximal MPS after exercise used leg-only workouts, whereas the present study used a whole-body workout protocol. This suggests that the greater overall amount of muscle mass activation during exercise may have an effect on protein requirements for maximal post-exercise protein synthesis.

The big picture

Since blood flow is known to increase following resistance exercise, which also increases amino acid transport and uptake into muscle cells, it seems reasonable to assume that the greater amounts of muscle mass involved would result in increased amino acid uptake and a resulting increase in the post-workout protein requirement for maximal MPS stimulation. This led the authors to propose that 20–25 grams of whey protein may be insufficient to promote maximal recovery from whole-body resistance exercise.

Although the increased amount of muscle mass used during whole-body workouts may account for differences from previous studies arriving at the 20–25 gram number for maximal MPS, the authors note other possible explanations. One of those differences may be attributed to sample size, which was larger in the present study (n=30) than previous work which used 12 and 6 participants. This is further supported by the fact that significance of MPS differences was not observed within the low LBM or the high LBM groups, but combining the two groups (and thus, increasing statistical power) did lead to a significant difference. It is possible that previous studies with smaller sample sizes lacked that statistical power to detect subtle, but real trends in the data.

Another explanation for discrepancies could be the type of protein ingested. This is unlikely however, given that the previous studies arriving at the “20–25 gram” number used different types of proteins and yet arrived at the same MPS number. Therefore, even after accounting for possible confounders, results from the present study suggest that exercise involving greater amounts of muscle mass may increase protein requirements for maximal acute activation MPS. The authors sum up their conclusions in the paper: “It seems that the overall amount of muscle mass possessed by the individual is a less important determinant of the maximally effective dose of protein to ingest than the amount of muscle mass activated during exercise.”

Taking the results of this study at face value, the implication is that the amount of muscle mass used during a given training session may dictate post-workout protein requirements for maximal activation of MPS after training. Although more research is needed with larger experimental groups, the evidence is sufficient to suggest that those consuming only 20–25 grams protein after training may benefit from 40 grams. This brings about some more practical, less academic considerations. To repair damaged muscle tissue after strenuous weight training and add new lean tissue as part of the adaptive process, a certain amount of high-quality protein is required. In the big picture, it is important to get enough of said high-quality protein. Getting “only enough” is of less importance, assuming there are no underlying health issues or dietary restrictions that contraindicate the increased amount of protein. At the best, bumping up post-workout protein consumption from 25 to 40 grams may be helpful. At the worst, “excess” protein is consumed: 60 extra kcals from 15 grams of additional protein will likely not disrupt even the most stringent of diets. Future research may determine how much protein is needed for different types of individuals in response to varying training methodologies.

Although more research is needed, the current study suggests that those consuming only 20–25 grams protein after training may achieve greater post-workout MPS with 40 grams.

Frequently asked questions

Is it important to ingest protein immediately after training?

The experimental model in the present study involved the intake of protein immediately after training. Whether or not this was absolutely necessary is a matter of debate. The existence of a post-workout “anabolic window” where growth and recovery are enhanced by taking in protein/nutrients within a certain time frame after training is a contentious topic in the literature.

On the one hand, it is well established that acute increases in muscle protein synthesis after training are greater with the ingestion of protein. On the other hand, it has yet to be established that this acute spike in protein synthesis after training is necessary for optimal growth and recovery over the long term. One thing that is certain is that all types of resistance exercise are associated with mechanical and metabolic stress that causes local damage to muscle tissue. Muscle cell membranes in particular are vulnerable to mechanical stress-induced damage that has to be fixed in order to maintain muscle function. Therefore, the recovery and adaptation process after exercise requires new protein synthesis to repair or replace oxidized/damaged proteins in muscle tissue. As long as researchers can agree on that, the debate over protein timing and the existence of the mythical “anabolic” window is more of an academic one. Ingesting protein right after training may or may not be absolutely necessary, but it can’t hurt.

Can we be sure that lean body mass is not a factor in protein dosage requirements?

Data in the present study suggests that lean body mass does not have an effect on the amount of protein needed for maximal protein synthesis after training. Instead, it was the whole-body workout protocol that seemed to account for the increase in MPS with the 40-gram versus 20-gram dose of protein. Operating under the assumption that this result was caused by the increased amount of muscle mass used during whole-body workouts relative to leg-only workouts in the earlier studies, it is possible that lean body mass could factor into this equation at some point.

As a thought experiment, compare a small, skinny adult with a lean mass of 70 pounds to a larger adult with 210 pounds of lean mass. If the total amount of muscle mass used is the ultimate determining factor for protein requirements, then all other variables being equal, the larger adult would have a higher post-workout protein requirement for maximal activation of MPS after training. More research is needed to answer this question with any kind of certainty.

What should I know?

An experimental model is always relevant when extrapolating the results of studies in the literature to real-life scenarios. Taking earlier studies at face value suggests that 20–25 grams of protein will elicit a maximal acute MPS response after training. Using a different exercise protocol (whole-body workouts as opposed to leg-only training) the authors in the present study noted that 40 grams of protein was superior to 20 grams for MPS, irrespective of lean body mass. The major take-away from this study is that the theoretical 25-gram limit for maximal acute post-exercise MPS is likely a product of the specific experimental models that arrived at that number. If you are performing whole-body workouts or stimulating large muscle groups with compound exercises, you may benefit from consuming more than 25 grams of protein after training.

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